1. Technical Field
This application relates to abrasive compacts with various physical characteristics, such as compacts having a continuous gradient, a multiaxial gradient, or multiple independent gradients.
2. Description of the Related Art
Abrasive compacts are widely used in drilling, boring, cutting, milling, grinding and other material removal operations. Abrasive compacts include ultra-hard particles sintered, bonded, or otherwise consolidated into a solid body. Ultra-hard particles may include natural or synthetic diamond, cubic boron nitride (CBN), carbo-nitride (CN) compounds, boron-carbon-nitrogen-oxygen (BCNO) compounds, or any material with hardness greater than that of boron carbide. The ultra-hard particles may be single crystals, polycrystalline aggregates or both.
In commerce, abrasive compacts are sometimes referred to as polycrystalline diamond (PCD), or diamond compacts when based on diamond. Abrasive compacts based on CBN are often called polycrystalline cubic boron nitride (PCBN) or CBN compacts. Abrasive compacts from which residual sintering catalysts have been partially or totally removed are sometimes called leached or thermally stable compacts. Abrasive compacts integrated with cemented carbide or other substrates are sometimes called supported compacts.
Abrasive compacts are useful for demanding applications requiring resistance to abrasion, corrosion, thermal stress, impact resistance, and strength. Design compromises for these abrasive compacts arise from the difficulty of attaching the abrasive compact to supporting substrates, sintering process limitations, or balancing inversely varying properties, such as the need for sintering additives and their effect on corrosion resistance. Prior art abrasive compacts use layered microstructures to overcome some of these design compromises. The prior art's transition between layers with different ultra-hard particle sizes is shown in FIG. 1, where a uniform fine particle region 111, with fine particles 114 and uniformly coarse region 112 and respectively 113, are visible. FIG. 2 shows the abrupt change in particle size of the compact of FIG. 1 that appears 550 microns from the active cutting surface of the cutter.
Prior art compacts also use abrupt chemical transitions. FIG. 3, an electron micrograph, illustrates a catalyst concentration change 213, 214 in a prior art supported abrasive compact. The catalyst metal depleted region 211 is near the active cutting surface 217. The catalyst metal is visible in the metal rich region 212 as a fine network of light gray lines. The transition also may be shown by electron beam microprobe analysis conducted along the line heading from one surface 215 to another 216. FIG. 4 graphically illustrates the five-fold reduction in catalyst concentration of the cutter of FIG. 3 along the line between surfaces 215 and 216. Both transitions take place over about one coarse grain diameter.
The abrupt transitions in physical properties or structure of prior art abrasive compacts are also supported by patent drawings of, for example, U.S. Pat. No. 5,135,061, U.S. Pat. No. 6,187,068, and U.S. Pat. No. 4,604,106, the disclosures of which are incorporated herein by reference in their entirety. The foregoing abrasive compacts all contain discrete layers of essentially uniform physical characteristics with abrupt transitions between the regions. Abrupt transitions in physical, chemical or structural characteristics can reduce performance of abrasive compacts.